1. Field of the Invention
The present invention relates to a thin film transistor (TFT) array used in an active matrix-type liquid crystal display (LCD) apparatus.
2. Description of the Related Art
An active matrix-type LCD apparatus is thin, so that it is often used in various display apparatuses. In this active matrix-type LCD apparatus, since individual pixel electrodes are independently driven, the contrast is not reduced based upon the reduction of a duty ratio, and also, the angle of visibility is not reduced, even when the capacity of display is increased to increase the number of lines.
In the active matrix-type LCD apparatus, one TFT is provided as a switching element for each pixel. A prior art TFT is constructed by a gate electrode formed on a transparent insulating substrate, a semiconductor active layer made of amorphous silicon opposing the gate electrode, a drain electrode and a source electrode connected to a transparent pixel electrode, which will be later explained in detail.
In the above-mentioned TFT used in an active matrix-type LCD apparatus, however, there is a large optical transmission area surrounding the semiconductor active layer. Therefore, light is incident from a backlight source through this optical transmission area to the semiconductor active layer. As a result, even when the TFT is in an OFF state, carriers are generated within the semiconductor active layer of the TFT to thereby increase an OFF current (leakage current) flowing therethrough. This may reduce the performance of the active matrix-type LCD apparatus.